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Printing a large‐area bismuth vanadate photoanode offers a promising approach for cost‐effective photoelectrochemical (PEC) water splitting. However, the light absorption trade‐off with charge transfer, as well as stability issues always lead to poor PEC efficiency. Here, the solution‐processed recipe is advanced with BiI3 dopant for the printed deposition with controllable crystal growth. The resultant BiVO4 films prefer (001) orientation with nanorod feature on substrate, allowing a faster charge transfer and improved photocurrent. The BiVO4 photoanode in tandem with perovskite solar module delivers an operating photocurrent density of 5.88 mA cm−2 at zero bias in 3.11 cm2 active area under AM 1.5 G illumination, yielding a solar‐to‐hydrogen efficiency as high as 7.02% for unbiased water splitting. Equally important, the stability of the aged BiVO4 rods has been addressed to distinguish phase segregation at surface. The photocatalysis degradation composes of vanadium loss and Bi2O3 enriching at the surface, opening a lid on the long‐term stability of BiVO4 photoanodes. [ABSTRACT FROM AUTHOR]

The concept of hybrid tandem device structures that combine metal oxides with thin‐film semiconducting photoabsorbers holds great promise for large‐scale, robust, and cost‐effective bias‐free photoelectrochemical water splitting (PEC‐WS). This work highlights important steps toward the efficient coupling of high‐performance hematite photoanodes with multijunction thin‐film silicon photocathodes providing high bias‐free photocurrent density. The hybrid PEC‐WS device is optimized by testing three types of multijunction silicon photocathodes with the hematite photoanode: amorphous silicon (a‐Si:H) tandem: a‐Si:H/a‐Si:H and triple junction with microcrystalline silicon (μc‐Si:H): a‐Si:H/a‐Si:H/μc‐Si:H and a‐Si:H/μc‐Si:H/μc‐Si:H. The results provide evidence that the multijunction structures offer high flexibility for hybrid tandem devices with regard to tunable photovoltages and spectral matching. Furthermore, both photoanode and photocathode are tested under various electrolyte and light concentration conditions, respectively, with respect to their photoelectrochemical performance and stability. A 27 % enhancement in the solar‐to‐hydrogen conversion efficiency is observed upon concentrating light from 100 to 300 mW cm−2. Ultimately, bias‐free water splitting is demonstrated, with a photocurrent density of 4.6 mA cm−2 (under concentrated illumination) paired with excellent operation stability for more than 24 h of the all‐earth‐abundant and low‐cost hematite/silicon tandem PEC‐WS device. Solar water splitting: An earth‐abundant and low‐cost hematite/silicon tandem hybrid photoelectrochemical water splitting (PEC‐WS) device is investigated. The combination of a nanostructured hematite‐based photoanode with a thin‐film silicon‐based photocathode gives rise to a considerable enhancement in the solar‐to‐hydrogen conversion efficiency as the light is concentrated from 100 to 300 mW cm−2. In addition, a bias‐free water splitting is demonstrated along with excellent operation stability for more than 24 h. [ABSTRACT FROM AUTHOR]

Water photolysis is a sustainable technology to convert natural solar energy and water into chemical fuels and is thus considered a thorough solution to the forthcoming energy crises. Unassisted water splitting that could directly harvest solar light and subsequently split water in a single device has become an important research theme. Three types of tandem devices including photoelectrochemical (PEC), photovoltaic (PV) cell/PEC and PV/electrolyser tandem cells are proposed to realize water photolysis at different levels of integration and component. Recent progress in tandem water splitting devices is summarized, and crucial issues on device optimization from the perspective of each photo-absorber functionalities in band edge potential, light absorptivity and transmittance are discussed. By increasing the performances of stand-alone PEC or PV devices, a 20% solar to hydrogen efficiency is predicted that is a significant value towards further application in practice. Accordingly, the challenges for materials development and configuration optimization are further outlined. [ABSTRACT FROM AUTHOR]